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Fertility Process

In vitro fertilization (IVF) is what comes to mind for most people when they think about infertility treatment. This is not surprising given the increasing use of IVF over the last 10 years.

The basic premise of all assisted reproductive technology (ART) is that the fertilization process (union of the sperm and egg) and embryo transfer process (placement of the embryo into the uterus) is aided by a fertility clinic laboratory. The IVF technique was initially designed for treatment of women with tubal infertility since the fallopian tubes are bypassed entirely with IVF. Eggs are retrieved from the body and inseminated in a lab with semen from a partner or a donor. The resulting embryos are transferred to the uterus in a separate procedure.

Egg Retrieval

Egg retrieval is performed about 36 hours after human chorionic gonadotropin (HCG) is given to mature the eggs. Light anesthesia is administered, and the eggs are usually removed by ultrasound guided retrieval or, less commonly, by laparoscopy. The follicles and the eggs and fluid which surround them are aspirated into a tube that is then given to the embryology lab (see below).

The procedure itself has minimal risks but post-operative cramping is common. Intra-abdominal bleeding and infection are two possible side effects however these are quite rare. Recovery time is generally short - one to one and a half hours.

Fertilization

The embryologist looks for eggs in fluid aspirated from the follicles. The eggs are assessed for maturity and incubated. The male partner is asked to collect a semen sample if fresh sperm is used. A semen analysis is performed and the sample is washed with a special solution of nutrients to isolate the more motile sperm. Fertilization is done in the lab. The exact process used depends on the type of infertility problem and clinic preferences. In standard IVF, the sperm is placed into the dish containing the egg. Some fertility clinics perform intracytoplasmic sperm injection (ICSI) routinely for reasons other than male infertility.

Embryo Transfer

Transfer usually occurs two to five days after fertilization depending on the number and quality of the embryos and the clinic policy. Healthcare providers will often transfer more than one embryo into the woman's uterus to increase the chances of pregnancy. However, the number transferred depends on the age of the woman, the quality of the embryos, and the success rates of the clinic. The current trend is to transfer one to two good embryos to reduce the risk of high order multiple pregnancy (triplets or more).

The embryo culture systems currently used allow the embryos to develop to the blastocyst stage (days 5-7) instead of days 2 to 3. The extra days in culture assist the embryologist in selecting better embryos for transfer. This means that fewer embryos (one to two usually) are transferred without compromising pregnancy rates. It also means that the risk of multiple pregnancy is reduced. The process of natural selection determines which embryos grow to the blastocyst stage since some will arrest before then. On average 40% to 50% of the fertilized embryos will continue developing into blastocysts.

For a couple to conceive, several biological processes need to take place successfully and at the right time. The following steps are necessary for conception to take place.

During her menstrual cycle, a woman's hormones stimulate the growth, maturation, and release of an egg from her ovary. This process begins when the hypothalamus signals the pituitary gland to send a hormone known as follicle-stimulating hormone (FSH) to the ovaries, prompting them to prepare an egg for ovulation. The FSH stimulates a group of follicles to grow on the surface of the ovary.

Over the next two weeks (the follicular phase of the cycle), the eggs mature and levels of estrogen, which is produced by the ovaries, increase.

As the estrogen levels increase, the pituitary gland decreases its production of FSH, and LH (luteinizing hormone) production is then triggered. The cervix begins to produce fertile alkaline mucus to help keep potential sperm alive and to speed their transport.

The LH production peaks, signaling the ovary to release a mature egg (usually only one) from its follicle in a process known as ovulation. The egg enters and begins to travel through the fallopian tube. The egg remains viable for about 24 hours.

For fertilization to occur, a sperm must locate and penetrate the awaiting egg while it is in the fallopian tube. If fertilization occurs, the fertilized egg, or embryo, continues to travel down the fallopian tube into the uterus.

On approximately the seventh day following fertilization, the embryo develops chorionic villi, which are special protrusions on its surface that enable it to attach, or implant, in the lining of the uterus.

The chorionic villi produce a hormone called human chorionic gonadotropin (hCG) that signals the corpus luteum to continue to increase in size and produce more progesterone to maintain the pregnancy; hCG is the hormone that is picked up by a pregnancy testing kit.